JPS59206803A - Optical fiber core - Google Patents

Abstract

PURPOSE:To reduce the transmission loss over a long distance and to increase the strength by using aromatic polyester having about 10<-6> deg.C<-1> coefft. of linear expansion as a secondary coating material for an optical fiber. CONSTITUTION:A thermoplastic resin coating an optical fiber strand is aromatic polyester subjected to molecular orientation at >=10<2>sec<-1> shear rate, having <=400 deg.C crystal/liq. crystal transition point, and contg. at least one kind of ring selected among 1,4-,1,2,4- and 1,2,4,5-substituted benzene rings and 2,6-substituted polynuclear aromatic rings in the principal polymer chain. The thermoplastic resin forming a secondary coating layer is not restricted to a polyethylene terephthalate-p-oxybenzoic acid copolymer. The resin is required only to have <=400 deg.C crystal/liq. crystal transition point. The upper limit temp. of a general extruder is 400 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber coated with a thermoplastic resin having a low coefficient of linear expansion.

Optical fiber is a fragile material with a diameter of 150 μm or less, so it is easy to get scratches on its surface during its manufacturing or cable production process, which becomes a source of stress concentration, and easily deteriorates when external stress is applied. It has the disadvantage of breaking. For this reason, in order to protect the optical fiber surface and maintain its initial strength, the fiber surface is coated with plastic immediately after spinning the optical fiber.

This plastic MW generally consists of a primary coating layer and a secondary coating layer. The primary coating layer is a material with a low Young's modulus, and its purpose is to maintain the initial strength of the optical fiber and to prevent an increase in fiber microbending loss due to non-uniformity of the secondary coating. On the other hand, the secondary coating layer is made of a thermoplastic resin such as polyamide or polyethylene, and is intended to facilitate handling in making cables and the like.

However, all conventional secondary coating materials have a much larger coefficient of linear expansion (on the order of 10°C) than that of the fiber itself (on the order of 10°C), so the secondary coating may Expansion and contraction of the fiber caused bending in the fiber, resulting in increased loss due to microbending.

In order to prevent an increase in microbending loss due to the difference in linear expansion coefficient between the secondary coating material and the fiber, glass fibers are arranged vertically in the length direction of the fiber with a silicone coating layer, and thermosetting resin is Harden and fix with
A fiber core having a second coating layer has been proposed. The coefficient of linear expansion of the secondary coating layer of this fiber core is on the order of 10° C., and the increase in microbending loss is significantly suppressed. However, the low coefficient of linear expansion of the secondary coating layer in this case is due to the coefficient of linear expansion of the glass fiber (on the order of 10°C), and the thermosetting resin itself has a large coefficient of linear expansion on the order of 10-4°C-1. There is no change in what I am doing.

The present invention focuses on the fact that the coefficient of linear expansion in the molecular orientation direction of an aromatic polyester exhibiting molten liquid crystallinity is 10°C or less, and is characterized in that this material is used as a secondary coating material for Hikari 7 Eyepa. The object of the present invention is to provide a coated optical fiber that has excellent transmission loss and high strength over a long length.

Certain crystalline polymers, when heated, may undergo a state of crystal anisotropy and liquid fluidity before melting and becoming a liquid. This state is called liquid crystal, and the temperature at which it changes from crystal to liquid crystal (or from liquid crystal to crystal) is called the crystal/liquid crystal transition point. The present inventors have already investigated coating an optical fiber wire by an extrusion method using a molten liquid crystalline thermoplastic resin that exhibits a crystal/liquid crystal transition point at a temperature lower than the thermal decomposition humidity. As a result, Tokugan Sho Is? -2146
It has been found that a resin extruded at a high shear rate of 10 sec or more as described in No. 82 exhibits a low coefficient of linear expansion on the order of 10°C.

As mentioned above, a thermoplastic resin exhibiting molten liquid crystallinity achieves a low coefficient of linear expansion through molecular orientation.

However, it has been found that the achieved coefficient of linear expansion is influenced not only by the shear rate but also by the extrusion conditions (extrusion temperature, structure of the extruded part).

Figure 1 shows polyethylene terephthalate (polyethylene terephthalate) exhibiting liquid crystallinity.
The relationship between linear expansion coefficient and shear rate when a PET)-p-oxybenzoic acid copolymer is molecularly oriented under appropriate extrusion conditions using a capillary rheometer is shown. The extrusion temperature at this time was 240° C., the capillary inner diameter was 0.5 mm, and the length of the shear orientation section was 10(8) mrn. As is clear from Fig. 1, the shear 6-
1. A low coefficient of linear expansion on the order of 10° C. has been achieved at a speed of 10 sec or more.

FIG. 2 is a cross-sectional view of one embodiment of the optical fiber core wire of the present invention, where l is a bare optical fiber, 2 is a primary coating layer made of a modified silicone rubber composition, and 8 is a primary coating layer made of a silicone rubber composition. 4 is an eighth coating layer made of a polyethylene terephthalate-T)-oxybenzoic copolymer. The thickness of each layer in Figure 2 is 85 to 40 mm for primary coating layer 2.
The 9m1 buffer layer 8 has a thickness of 100 μya, and the secondary coating layer 4 has a thickness of 250 μm. The secondary coating layer 4 has a die diameter of 2 mm.
, using an extruder having an extrusion section with a nipple diameter of 1 or 2 trwn and a linear length of the die outlet lOt'1vrn, at an extrusion temperature (die outlet temperature) of 240°C, I
It was formed by extrusion at a shear rate of 0 ago. The transmission loss at 20° C. when only the primary coating layer and buffer layer 8 are provided (at the strand stage) is 8.406 B/km at a wavelength of 0.85 #ya, and the fiber core according to the present invention has a transmission loss of 8.406 B/km at a wavelength of 0.85 #ya. At a wavelength of 0.85 μm, the transmission loss was 2.41 eiB/km at 80°C.

FIG. 8 shows the temperature dependence of the transmission loss of the core wire according to the present invention. As shown in Figure 8, from -60℃ to +60℃
There is no increase in loss in the core wire. In addition, the average breaking strength of the core wire is 496 kg 7 mm (sample length 10 mm, number of samples 20)
Met.

The thermoplastic resin forming the secondary coating layer in the present invention is
It is not limited to polyethylene terephthalate-p-oxybenzoic acid copolymer, but is formed from liquid crystal polymers that have a crystal/liquid crystal transition point at a temperature lower than 400°C, which is the upper limit temperature of a general extruder. Ru. Specific materials include polymer main chain ni 1,4-mot, kuha 1.2.4- or 1.2.4. Is -substituted benzene ring or 2,6
- Aromatic polyesters containing substituted polynuclear aromatic rings, such as terephthalic acid-p-oxyphenol-polyethylene terebutyrate copolymers, polyethylene terephthalate-
p-oxybenzoic acid copolymer, terephthalic acid-2-chloro-4-oxyphenol-4,4'-oxydiphenol copolymer, terephthalic acid-p-oxyphenol-z, 6-naphthalene dicarboxylic acid copolymer Combined, prephthalic acid-2,5-dimethyl-4-oxyphenol-4,4
'-diphenol copolymer, 2yx=4-oxyphenol-terental acid copolymer, and the like can be used.

As explained above, in the present invention, aromatic polyester having a coefficient of linear expansion on the order of approximately 10° C. is used as the secondary coating material of the optical fiber, so that the optical fiber has excellent transmission loss over a long length and high strength. A fiber core can be obtained. -4. Brief explanation of the drawings Fig. 1 is a diagram showing the relationship between coefficient of linear expansion and shear rate, Fig. 2 is a sectional view showing the structure of the optical fiber core wire of the present invention, and Fig. 8 is a diagram showing the relationship between coefficient of linear expansion and shear rate. FIG. 3 is a diagram showing the relationship between the increase in loss at 0.85 μm and the measured temperature of the optical fiber core wire.

1... Optical fiber ridge line, 2... Primary observation layer, 8...
- Buffer layer, 4... secondary coating layer.

(β., -〇nonlakuii <*y 4→1-1
too

Claims (1)

[Claims] 1. In an optical fiber core wire having a structure in which the optical fiber wire is coated with a thermoplastic resin, the thermoplastic resin is coated with 1
The molecules are oriented at a shear rate of 0 sec or more, have a crystal/liquid crystal transition point at temperatures as low as 400°C, and have 1.4- or 1, B, 4 in the polymer main chain.
- or 1, 2.4.3-substituted benzene ring or 2
．． An optical fiber core wire characterized in that it is an aromatic polyester containing at least one type of 6-substituted polynuclear aromatic ring.